Electroluminescent information display system



Feb. 18, 1964 s. TALESNICK 3,121,824

ELECTROLUMINESCENT INFORMATION DISPLAY SYSTEM 3 Sheets-Sheet 1 Filed June 16, 1960 INVENTOR v SIDNEY MLES/V/C'K R.}.61W/

ATTORNEY Feb. 18, 1964 3 Sheets-Sheet 2 Filed June 16, 1960 TTOR NEY Feb. 18, 1964 S. TALESNICK ELECTROLUMINESCENT INFORMATION DISPLAY SYSTEM Filed June 16, 1960 Sheets-Sheet 3 TRIGGER GEN. 3 REFERENCE 2 A GPA/.25 2! A A H2 I COMPARATOR 27 mum/enroll 2! I COMPARATOR 29 6+ n H COMPARATOR 30 ip l 38 37 SAM/7007f! GEM 2/ gnu 700m M?! 4 "q /I\/ $AW7'007/l GEN-2? l v .sAwraar/l 651v. 24 fD 1 my. 5 I I I I TRIGGER GEN. 20

REFERENCE 1 /I GE/V- Z5- 76 80' ERAS'E RECORD f f H H H L 1 U [J F amaz I XAMPL/F/ER 40 q 2 x .smmm 42 l r J U H I 6 6 INVENTOR SIDNEY TALESW/CK ATTORNEY United States Patent 3,121,824 ELEfiTRGLUh IEWESCENT INFGRMATION DISPLAY SYSTEM Slidney Talesnick, Brooklyn, N.Y., assignor to General Telephone and Electronics Laboratories, End, a corporation of Delaware Filed June 16, 1960, Ser. No. 36,663 11 Claims. (6!. 315-469) This invention relates to information display systems.

in the copending patent application Serial No. 36,665, filed June 16, 1960', by Stephen Yando, there is disclosed an electroluminescent device for visually displaying applied input signals as discrete points on an electroluminescent panel. In one embodiment, this device comprises a rectangular electroluminescent phosphor layer atfixed to one surface of a rectangular sheet of piezoelectric material. The piezoelectric sheet is provided with first and second parallel edges and third and fourth parallel edges, the third and fourth parallel edges being located between and perpendicular to the first and second edges. The surface area of the electroluminescent layer is less than that of the piezoelectric sheet and its sides are parallel to the edges of the sheet. A transparent conductive electrode is placed over the electroluminescent layer while a common grounded electrode is secured to the other side of the piezoelectric sheet.

First, second, and third. electrodes are secured to the piezoelectric sheet between its first, second, and third edges respectively and the electroluminescent layer. Thus, the first and second electrodes are parallel to each other and adjacent to opposite sides of the electroluminescent layer while the third electrode is perpendicular to the first and second electrodes. All four edges of the sheet are provided with terminations which absorb, substantially without reflection, any incident elastic waves.

A first voltage pulse applied between the first electrode and the grounded electrode produces a mechanical strain in the piezoelectric sheet proportional to the amplitude of the first pulse. As the strain changes, a disturbance in the form of a first plane elastic wave accompanied by a first electric field, is propagated from the first electrode toward the opposite edge of the sheet where it is absorbed by the termination. The intensity of the electric field is proportional to the time rate of change of the strain that produced it; i.e. the intensity of the first electric field is proportional to the first time derivative of the first pulse.

Similarly, second and third voltage pulses applied between the second and third electrodes respectively and the grounded electrode produce second and third plane elastic waves. Each of these waves is accompanied by an electric field which is propagated from the corresponding electrode toward the opposite edge of the sheet where it is absorbed. The intensity of the second electric field is proportional to the first time derivative of the second voltage pulse, while the intensity of the third electric field is proportional to the first time derivative of the third voltage pulse.

By applying voltage pulses to all three electrodes simultaneously, three elastic Waves are generated which intersect in a small region near the center of the square electroluminescent layer. The intensities of the three electric fields produced by the three waves are additive, resulting in a bright spot of light at the center of the layer. By adjusting the relative timing of the voltage pulses applied to each of the three electrodes, any selected area of the electroluminescent layer may be caused to glow. Further, by continuously varying the relative timing of the three pulses, the spot of light can be caused to scan the panel at a velocity determined by the timing of the applied pulses.

In another form of the display device, a fourth electrode is secured to the piezoelectric sheet between the fourth edge of the sheet and the electroluminescent layer. A voltage pulse applied between this electrode and ground produces a fourth elastic wave accompanied by an electric field which propagates from the fourth electrode toward the opposite edge of the sheet where it is absorbed. By applying the voltage pulse to the fourth electrode at the correct instant of time relative to the time of application of pulses to the other three electrodes, the four waves are caused to intersect upon the selected point resulting in a bright spot of light in the electroluminescent layer at this point. Since the electric fields are additive, the use of four Waves instead of three results in a brighter and more intense image.

In order to obtain the maximum resolution and accuracy from this device, the voltage pulses must be applied to the electrodes at precise time intervals dependent upon the input data and the characteristics of the piezoelectric sheet and the electroluminescent layer. Further, apparatus must be provided for sampling varying input voltages at a rate limited only by the velocity of the elastic waves in the piezoelectric sheet and by the width of the electroluminescent layer.

Accordingly it is an object of this invention to provide an improved information display system in which an applied signal may be visually and accurately displayed.

Another object of the invention is to provide an information display system in which the magnitudes of a pair of applied signals may be displayed as a single point relative to a pair of coordinate axes superimposed on an electroluminescent panel.

Still another object is to provide an information display system in which a varying input signal is sampled and periodically applied to an electroluminescent display panel.

A further object is to provide an extremely accurate information display system having high resolution which is relatively simple and inexpensive to manufacture.

In the present invention, there is provided an information display system in which voltage pulses are applied to the n electrodes of an electroluminescent display device of the type disclosed in the aforementioned application Serial No. 36,665. Each of these voltage pulses produces an elastic wave, accompanied by an electric field, which is propagated through the piezoelectric sheet. By properly timing the application of each pulse, the Waves are made to intersect at a predetermined spot in the electroluminescent phosphor layer thereby causing the phosphor to glow at the point of intersection.

A pulse tirnhig circuit comprising a reference generator, a computer, it voltage comparators, and n pulse shaping circuits, is utilized in generating the voltage pulses. One of the voltage comparators is controlled by the reference generator and a fixed input voltage, its function being to generate pulses for application at fixed periodic intervals to one of the n electrodes on the display device. The remaining voltage comparator-s are coupled to both the reference generator and the computer.

Input signals applied to the computer are converted therein to nl voltage functions of the input signal. Each of these n-1 voltage functions is applied to one of the remaining voltage comparators where it is compared with the output of the reference generator. When the reference generator output voltage and the computer output voltage applied to a particular voltage comparator attain a predetermined relationship to each other, the

voltage comparator produces an output pulse which is coupled through a pulse shaping circuit to a corresponding electrode. Since each of the 111 outputs from the computer has, in general, a different magnitude, each of the voltage comparators is triggered oil at a different time. As will be shown hereinafter, the voltage comparator pulses are initiated by the computer at the precise instants of time required to accurately exhibit the input data on display device.

If the input signals are invariant with time, they may e applied directly to the computer. However, if the in put signals are changing with time, they must be sampled periodically and stored for subsequent application to the computer. Accordingly, each input signal is applied to the computer through sampling and memory circuits. An erase-record generator controls the sampling and memory circuits initiating the removal of information already fed to the computer and the transfer of newly stored informa tion to the computer.

In one embodiment of the invention three channels, each including a voltage comparator and a pulse shaping circuit, are coupled to three corresponding electrodes on the display device. By launching waves from the three electrodes with the proper time displacement, they may be made to intersect at any point on the display panel thereby producing an illuminated spot. The brightness of the spot may be increased by adding a fourth electrode and associated voltage comparator and pulse shaping circuits.

The above objects of and the brief introduction to the present invention will be more fully understood and further objects and advantages will become apparent from a study of the following description in connection with the drawings, wherein:

FIG. 1 is a cut-away perspective view of one type of display device used in the information display system;

FIG. 2 is a block diagram ot the information display system including a partial plan view of the displa device of FIG. 1;

FIG. 3 depicts voltage waveforms useful in explaining the operation of the system of FF. 2;

FIG. 4 is a simplified schematic diagram of one of the sampler circuits; and

FIG. 5 illustrates additional voltage waveforms occurign in the circuits of FIGS. 2 and 4.

Referring to FIG. 1 there is shown a thin, square, polar ized, ceramic piezoelectric sheet 1% comprising a lead titanate-lcad zirconate mixture. An electroluminescent layer 11, having a square surface area smaller than that of the piezoelectric sheet id, is placed in intimate contac with one surface of the sheet. A transparent conductive electrode 12 is affixed to the electroluminescent layer ll while a common grounded electrode 13 is secured to the opposite side of the piezoelectric sheet 16. Each edge of the sheet is terminated in such manner as to absorb, substantially without reflection, any incident elastic wave propagated in the sheet. This is accomplished by coating the edges and imme iately adjacent portions of sheet 1t) with lead to provide terminations 14, 15, 16 and 17.

A first electrode A extending across the entire width of ti e electroluminescent layer 11 is secured to the piezoelectric sheet between the terminations l4 and the edge of the layer 11. Similarly, electrodes B, C, and D are secured to the piezoelectric sheet 16 between terminations 15, i6, and 17 respectively and the electroluminescent layer 11. While four electrodes have been illustrated in order to provide an image having increased brightness, it shall be understood that three electrodes are sufficient to uniquely define any point on the electroluminescent phosphor layer 11.

The application of a voltage pulse between electrode A and grounded electrode 13 causes a first elastic wave to be propagated across the piezoelectric sheet 16 at constant speed toward absorbing termination 15. This wave is accompanied by an electric field having an intensity proportional to the time rate of change of the pulse applied to electrode A. A reverse wave also emanates from electrode A but is absorbed by termination 14 without affect ing the display. Similarly, voltage pulses applied to electrodes B, C, and D cause second, third, and fourth elastic waves, accompanied by corresponding electric fields, to be propagated at the same speed as the first wave toward terminations 14, 17, and 16 respectively.

When voltage pulses are applied to the four electrodes A-D simultaneously, the four elastic waves meet at the center resulting in a spot of light in the electroluminescent layer 11 having a brightness proportional to the total electric field produced by the four waves. By applying voltage pulses to electrodes A-D at different instants of time, the four waves can be made to intersect at any selected point on the electroluminescent layer.

In FIG. 2 there is shown a block diagram of the information display system together with a plan view of the display device. Although all of the blocks are illusrated as connected by a single lead, it will be understood that each component is connectcd to a common ground point and that all voltages are measured with respect to this ground. The electroluminescent layer 11, together with its conductive film 12, is 2s units on each side and each electrode is spaced r units from the edge of the layer 11. Also, the velocity of propagation of the elastic waves through the piezoelectric material 10 in all directions has a constant magnitude v. Coordinate axes x and v, having their origin at the center of the electroluminescent layer, are superimposed on the display device to provide a reference for defining points on the face of layer 11.

A point P, located x units to the right of the origin and y units above the origin, has been arbitrarily selected as the point to be illuminated. (Although the illuminated area is considered to be a point, it is actually a square having a length on each side of 30-40 mils or less.) In order to display a selected point such as P, voltage pulses must be applied to the electrodes AD at specific intervals of time which will permit the elastic waves propagated through the piezoelectric sheet 16 to intersect simultaneously upon the point.

The application of voltage pulses to the display device is initiated by a trigger generator 20 at a time arbitrarily designated as t-O. After a fixed time delay t a pulse is applied to electrode A by sawtooth generator 21 and an elastic wave, accompanied by an electric field, is propagated through the piezoelectric sheet 10 toward point P. The fixed delay t is equal to the time required for a wave to travel the distance 2s from one side of the electroluminescent layer to the opposite side. This delay is provided to permit a point located along the left hand side 35 of the electroluminescent layer to be displayed. To display such a point, a wave must leave electrode B with such timing as to traverse the distance r+2s and arrive :at edge 35 simultaneously with the arrival of the wave from electrode A; the wave from electrode A having traveled the relatively short distance r.

The time (measured from 1:0) required for a wave originating at electrode A to arrive at the point P is where in order for an elastic wave originating at electrode B to arrive at point P at time 1 it must leave electrode B at a time interval t after the trigger pulse.

Similarly, a wave must leave electrode C at a time for all four waves to arrive simultaneously at point P.

Referring to FIGS. 2 and 3, trigger pulses are applied periodically by trigger generator 2t) to the input of a reference generator 25. These trigger pulses (FIG. 3a) are generated at intervals equal to 3t this interval corresponding to the maximum time required for all four elastic waves to completely clear the display'area regardless of the location of the point P. Each trigger pulse initiates a sawtooth output voltage (-FIG. 3b) from reference generator 25 which is applied through a lead 26 to voltage comparators 2'7, 28, 29, and 30. The duration of each reference sawtooth is equal to Zt the time between adjacent sawtooth voltages being z Voltage comparators 27-30 may be of the type em ploying two input and one output connections as shown in FIGS. 9-6, page 332 of the book Waveforms by Chance et :al., published by McGraw-Hill Book Co. When the two input voltages are equal, an output voltage pulse is initiated which continues at a constant magnitude until one of the inputs is reduced to Zero. Thus, the sawtooth output voltage of reference generator 25 is fed to one input of voltage comparator 27 While a fixed voltage E proportional to the delay time t is coupled to the other input. When the sawtooth voltage 31 (FIG. 3b) rises to a value equal to the applied voltage E a pulse 32. (FIG. 30) is generated by voltage comparator 27. Pulse 32 is cut off whenthe reference sawtooth falls to zero. Pulse 32 is then differentiated in ditferentiator 33, the negative pulse produced by the trailing edge of pulse 32 removed by clipperamplifier 34, and the remaining positive pulse applied to multivibrator 36 which generates a pulse of suificient amplitude and duration to trigger sawtooth generator 21.

The output of sawtooth generator 21 is applied to electrode A. 'It comprises a first sawtooth portion 37 (FIG. 3g) having a steep negative slope and a second sawtooth portion 38 having a more gradual positive slope. Triggering of the first sawtooth portion 37 occurs coincidently with the leading edge of the output 32 of Voltage compmator 27 and therefore is delayed by an Since the magnitude of the electric field accompanying the elastic wave in the piezoelectric sheet is proportional to the derivative of the applied voltage, the rapidly changing sawtooth 37 produces a large electric field in the layer 11. The relatively slowly changing sawtooth portion 38 has a much smaller derivative and, therefore, any electric field produced by it has no significant effect on the display.

Two input signals x and y, which determine the location of the point P, are applied through amplifiers 49, 41 and x and y samplers 42, 43 respectively to the input of a computer 44. Computer 44, using conventional analog computer circuitry, produces first, second, and third output voltages proportional to t t and 13 respectively in accordance with Equations 2, 3 and 4. The first output of computer 44 is coupled by a lead 45 to voltage comparator 23 where its magnitude is compared with the magnitude of the reference sawtooth produced by generator Q5. When the reference sawtooth (FIG. 315) becomes equal to the first computer output, a pulse (FIG. 3d) is produced by comparator 23 which triggers sawtooth generator 22 through pulse shaping circuits 46. As shown in FIG. 3h, the rapidly changing portion 47 of the output of sawtooth generator 22 is initiated an interval t alter the trigger pulse, this voltage being applied to electrode B.

Similarly, the second and third outputs of computer 4% are connected to voltage comparators 29 and 3% by leads 48 and 4-9 respectively. When the reference sawtooth applied to the inputs of comparators 29 and 30 equals the second and third computer output voltages, the pulses shown in FIGS. 32 and 3 respectively are generated. These pulses are coupled through pulse shaping circuits 54 and 51 to sawtooth generators 2-3 and 24 respectively having the output voltage Waveforms shown in FIGS. 31' and 3 j. Thus, voltages are applied to electrodes AD at precisely the instants of time required to have the elastic waves converge simultaneously on point P.

As previously stated, any point on the electroluminescent layer it may be defined and displayed using only three electrodes. However, the use of four electrodes provides greater brightness and this increased brightness is sufiici-en t in some application to justify the use of additional components. Also, it shall be noted that the elastic waves generated by each of the pairs of perpendicular electrodes produce diagonal lines across the electroluminescent layer 11 which may appear faintly in the background. However, the point of intersection P of the three or four waves is suiliciently brighter than these spurious lines to prevent any significantly adverse effect on the readability of the display.

it the magnitudes of the x and y input signals are invariant with time, they may be connected directly to the input terminals of computer 44 without first being applied to samplers 42 and 43. However, if the inputs are changing with time, they must be sampled periodically in order to provide constant amplitude signals for comparators 284%. This is accomplished by sampling the outputs of x and y amplifiers 4d, 41 once during each cycle of trigger generator 20 and applying the outputs of samplers 42 and 43 to the input of computer 44-.

A schematic diagram of the circuit of x sampler 42 is shown in F1}. 4. The circuit of y sampler 43 and its mode of operation is identical to that of x sampler 42 and therefore has not been illustrated. x sampler 42 is coupled by means of a terminal on to the output of amplifier 413 and by a terminal d1 to the output of the erase-record generator s2 (FIG. 2). Terminal as is coupled through a resistor 64- and a diode 65 to an output terminal 66, while terminal or is coupled through a resistor 67 and capacitor 6-8 to the output terminal cs. A bias voltage source 69 having a constant magnitude V is connected to output terminal 66 through a resistor 7d and a diode 71. Resistors 64, 67, and 7d are small in magnitude and may comprise the internal impedances of the associated voltage sources. As shown in FIGS. 5]) and 5c, the erase-record generator 62 is triggered by the trailing edge of the output voltage of reference generator 25. The output of erase-record generator 62 comprises a short positive pulse having a magnitude V followed by a short negative pulse having the same magnitude.

The output of x amplifier ll is shown in HG. 5d. This voltage corresponds to the input signal and is arbitrarily assumed to have a sawtooth waveiorm and a he quencywhich is low compared to the repetition rate of the trig er generator 20. The output of amplifier 49 comprises A.-C. component having a zero average value and a D.-C. component having a value V/2. The bias voltage V/2 has been introduced to assure that with zero input the spot will be at the center of the display. By adjusting the magnitude of this bias voltage the position of the spot on the panel may be shifted. The maximum amplitude of the A.-C. component is limited to V/ 2 by adjusting the gain of amplifier 4h.

Assuming that the signal shown in FIG. 5d is applied at time t=0, and that no erase-record pulses have yet been applied to the system, capacitor 68 (FIG. 4) will be initially uncharged. Since the output of erase-record generator 62 is initially zero and capacitor 68 has no voltage across it, the voltage at output t rminal 66 will be zero as shown at in FIG. 5e. When the positive 6 pulse 76 5c) is applied to terminal 61, the voltage across capacitor 68 is instantaneously increased to a value V and therefore the output of x sampler 42 also rises to a value V as shown at 77.

The positive erase-record generator pulse '76 is abruptly followed by a short negative pulse 78 causing diode 65 to conduct and the voltage on o tput terminal 65 to drop to a value equal to the voltage (-V-lapplied to terminal 60 by amplifier 4% The output of erase-record generator 62 then rises abruptly to zero and the voltage stored across capacitor 68 is held at the value e as shown in FIG. 52.

T he next positive pulse St applied by erase-record generator 62 causes diode 71 to conduct. This clamps the voltage between output terminal 66 and ground at the value V and discharges capacitor 6% through resistor 7%. The erase-record generator 62 then produces a negative pulse 31 which cuts off diode 71 and causes diode to conduct charging capacitor 68 to a value 6 When the erase-record pulse 62 returns to zero, the voltage on terminal 66 increases to the value e Thus, as shown in FIG. 5, the input voltage applied to amplifier 4t is periodically sampled and constant magnitude step voltages obtained are used to determine the launching times of the elastic waves from electrodes AD.

The signals applied to the display device by electrodes A-D may be amplitude modulated by coupling a modulation signal M to sawtooth generators 21-24 by means of an amplifier In addition the display device may also be modulated by applying a voltage between transparent electrode 12 and the comrnon grounded electrode 13.

As many changes could be made in the above construction and many difierent embodiments could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An information display system comprising a sheet of piezoelectric material, an electroluminescent layer affixed to the surface of said sheet, at least three electrodes secured to the surface of said sheet adjacent said electroluminescent laycr, two of said electrodes ext nding along opposite sides of said electroluminescent layer and a third of said electrodes extending between said two electrodes, reference voltage means, computing means having a plurality of output terminals, said computing means producing a plurality of output voltages in response to applied input voltage signals, the magnitude of each of said output voltages being proportional to the time required for an elastic wave to travel through said piezoelectric sheet from a corresponding one of said electrodes to a point on said electroluminescent layer, said output voltages being functions of said applied input voltage signals, a like plurality of voltage comparators each having first and second inputs, said first inputs being coupled to said reference voltage means, means coupling each of the output terminals of said computing means to the second input of a corresponding one of said voltage comparators, each of said voltage comparators producing an output voltage when the voltage applied to its first input bears a predetermined ratio to the voltage applied to its second input, and means coupling the output of each of said voltage comparators to a corresponding one of said electrodes.

2. An information display system comprising a sheet of piezoelectric material; an electroluminescent layer affixed to the surface of said sheet; first, second and third electrodes secured to the surface of said sheet adjacent said electroluminescent layer, said first and second electrodes being parallel to each other and affixed to the surface of said sheet adjacent opposite sides of said electroluminescent layer and said third electrode being located adjacent said electroluminescent layer and perpendicular to and between said first and second electrodes; reference voltage means; computing means responsive to the magnitudes of first and second applied input voltage signals and producing first and second output voltages, each of said output voltages being proportional to the time required for an elastic wave to travel through said piezoelectric sheet from a corresponding one of said electrodes to a point on said electroluminescent layer, said first and second output voltages being functions of said first and second applied input voltage signals; first, second, and third voltage comparators each having first and second inputs, said first inputs being coupled to said reference voltage means, means coupling the first and second output terminals of said computing means to the second inputs of said second and third voltage comparzu tors respectively, the second input of said first voltage comparator being adapted to receive a fixed input voltage, each of said voltage comparators producing an output voltage pulse when the voltage applied to its second input bears a predetermined ratio to the output of said reference voltage source, and means coupling said first, second, and third voltage comparators to said first, second, and third electrodes respectively.

3. An information display system as defined in claim 2 wherein the voltage produced at the first output terminal of said computer is a function of said first applied input voltage signal and the voltage produced at the second output terminal of said computer is a function of said first and second applied input voltage signals.

4. An information display system comprising a sheet of piezoelectric material; an electroluminescent layer affixed to the surface of said sheet; first, second, third, and fourth electrodes secured to the surface of said sheet adjacent said electroluminescent layer, said first and second electrodes being parallel to each other and atfixed to the surface of said sheet adjacent opposite sides of said electroluminesccnt layer and said third and fourth electrodes being parallel to each other and afiixed to the surface of said sheet adjacent opposite sides of said electroluminescent layer, said third and fourth electrodes being located between and perpendicular to said first and second electrodes; reference voltage means; computing means responsive to the magnitudes of first and second applied input voltage signals and producing first, second and third ouput voltages, each of said output voltages being proportional to the time required for an elastic wave to travel through said piezoelectric sheet from a corresponding one of said electrodes to a point on said electroluminescent layer, said first, second and third output voltages bcing functions of said first and second applied input voltage signals; first, second, third and fourth voltage comparators each having a first and second input, said first input being coupled to said reference voltage means; means coupling the first, second and third output terminals of said computing means to the second inputs of said second, third, and fourth voltage comparators, the second input of said first voltage comparator being adapted to receive a fixed input voltage, each of said voltage comparators producing an output voltage pulse when the voltage applied to the second input bears a predetermined ratio to the output of said reference voltage source; and means coupling said first, second, third, and fourth voltage comparators to said first, second, third, and fourth electrodes respectively.

5. An information display system as defined in claim 4- wherein the voltage produced at the first output terminal of said computer is a function of the first input voltage signal and the voltages produced at the second and third output terminals of said computer are functions of said second and third applied input voltage signals.

6. An information display system for displaying applied input voltage signals comprising a sheet of piezoelectric material, an electroluminescent layer affixed to the surface of said sheet, at least three electrodes secured to the surface of said sheet adjacent said electroluminescent layer, two of said electrodes extending along opposite sides of said electroluminescent layer and a third of said electrodes extending between said two electrodes, reference voltage means, computing means producing a plurality of output voltages, each of said voltages being proportional to the time required for an elastic wave to travel through said piezoelectric sheet from a corresponding one of said electrodes to a point on said electroluminescent layer, said output voltages being functions of said applied input voltage signals, a plurality of voltage comparators each having first and second inputs, said first inputs being coupled to said reference voltage means, means coupling each of the output terminals of said computing means to the second input of a corresponding one of said voltage comparators, sampling means adapted to receive said applied input voltage signals coupled to said computing means, said sampling means periodically applying a voltage proportional to the instantaneous value of said input voltage signal to said computing means, and means coupling the output of each of said voltage comparators to a corresponding one of said electrodes.

7. An information display system for displaying first and second applied input voltage signals comprising a sheet of piezoelectric material, an electroluminescent layer affixed to the surface of said sheet, first, second, and third electrodes secured to the surface of said sheet adjacent said electroluminescent layer, said first and second electrodes being parallel to each other and afllxed to the surface of said sheet adjacent opposite sides of said electroluminescent layer and said third electrode being located adjacent said electroluminescent layer and perpendicular to and between said first and second electrodes, reference voltage means, computing means producing first and second output voltages, each of said first and second output voltages being proportional to the time required for an elastic wave to travel through said piezoelectric sheet from a corresponding one of said electrodes to a point on said electroluminescent layer, said first and second output voltages being functions of said first and second applied input voltage signals, first, second, and third voltage comparators each having first and second inputs, said first input being coupled to said reference voltage means, means coupling the first and second output terminals of said computing means to the second input of said second and third voltage comparators, the second input of said first voltage comparator being adapted to receive a fixed input voltage, first and second sampling means adapted to receive first and second applied input voltage signals coupled to said computing means, said sampling means periodically applying first and second voltages proportional to the instantaneous voltages of said first and second input voltage signals to said computing means, and means coupling said first, second, and third voltage comparators to said first, second, and third voltages respectively.

8. An information display system comprising a sheet of piezoelectric material, an electroluminescent layer affixed to the surface of said sheet, 11 electrodes secured to the surface of said sheet adjacent said electroluminescent layer where n equals at least three, two of said electrodes extending along opposite sides of said electroluminescent layer and a third of said electrodes extending between said two electrodes, 11 sawtooth generators each having its outputs coupled to a corresponding one of said It electrodes, reference voltage means having a recurrent linearly increasing output voltage, n voltage comparators each having first and second inputs, said first inputs being coupled to said reference voltage means, computing means having n-l output terminals coupled to the second inputs of n-1 of said voltage comparators, each of said voltage comparators producing an output voltage when the voltage applied to its first input bears a predetermined ratio to the voltage applied to its second input, means for coupling m input Voltage signals to the input of said computing means, said computing means producing at its n'l output terminals voltages which are functions of said In input voltage signals, each of said n-1 voltages being proportional to the time required for an elastic wave to travel through said piezoelectric sheet from a corresponding one of said electrodes to a point on said electroluminescent layer and 11 pulse shaping circuits coupling the output of said It voltage comparators to the inputs of said n sawtooth generators.

9. An information display system as defined in claim 8 wherein said means for coupling input voltage signals to the input of said computing means comprises in sampling means each having first and second inputs and an output coupled to said computing means, means for applying each of said In signals to the first input of a corresponding one of said sampling means, erase-record means coupled to said reference voltage means and to the second inputs of each of said sampling means, said erase-record means providing a first voltage to said sampling means for erasing input data stored therein and a second voltage for storing input .data corresponding to the input voltage signal concurrently applied to the first input of said sampling means.

10. An information display system as defined in claim 8 wherein modulation means responsive to an applied modulation signal is coupled to each of said It sawtooth generators.

11. An information display system comprising a sheet of piezoelectric material; a rectangular electroluminescent layer fixed to the surface of said sheet, said electroluminescent layer having first and second parallel edges and third and fourth parallel edges perpendicular to said first and second parallel edges; first, second, third and fourth linear electrodes secured to the surface of said sheet adjacent the first, second, third and fourth edges respectively of said electroluminescent layer; reference voltage means; computing means responsive to the magnitudes of first and second applied input voltage signals and having first, second, and third output terminals, the voltage produced at said first computer output terminal being proportional to the magnitude of said first applied input voltage signal, the voltage produced at said second computer output terminal being proportional to the difference between the magnitudes of said first and second input voltage signals, and the voltage produced at said third computer output terminal being proportional to the sum of the magnitudes of said first and second input voltage signals; first, second, third and fourth voltage comparators each having first and second inputs, said first inputs being coupled to said reference voltage means; means coupling the first, second, and third output terminals of said computing means to the second inputs of said second, third and fourth voltage comparators respectively; means coupling a fixed input voltage to the second input of said first voltage comparator, each of said voltage comparators producing an output voltage pulse when the voltage applied to its second input is equal to the output voltage of said reference voltage source; and means coupling said first, second, third and fourth voltage comparators to said first, second, third and fourth electrodes respectively.

References Cited in the file of this patent UNITED STATES PATENTS 2,816,236 Rosen Dec. 10, 1957 2,922,923 Yando Jan. 26, 1960 2,951,168 Yando Aug. 30, 1960 3,035,200 Yando May 15, 1962 

1. AN INFORMATION DISPLAY SYSTEM COMPRISING A SHEET OF PIEZOELECTRIC MATERIAL, AN ELECTROLUMINESCENT LAYER AFFIXED TO THE SURFACE OF SAID SHEET, AT LEAST THREE ELECTRODES SECURED TO THE SURFACE OF SAID SHEET ADJACENT SAID ELECTROLUMINESCENT LAYER, TWO OF SAID ELECTRODES EXTENDING ALONG OPPOSITE SIDES OF SAID ELECTROLUMINESCENT LAYER AND A THIRD OF SAID ELECTRODES EXTENDING BETWEEN SAID TWO ELECTRODES, REFERENCE VOLTAGE MEANS, COMPUTING MEANS HAVING A PLURALITY OF OUTPUT TERMINALS, SAID COMPUTING MEANS PRODUCING A PLURALITY OF OUTPUT VOLTAGES IN RESPONSE TO APPLIED INPUT VOLTAGE SIGNALS, THE MAGNITUDE OF EACH OF SAID OUTPUT VOLTAGES BEING PROPORTIONAL TO THE TIME REQUIRED FOR AN ELASTIC WAVE TO TRAVEL THROUGH SAID PIEZOELECTRIC SHEET FROM A CORRESPONDING ONE OF SAID ELECTRODES TO A POINT ON SAID ELECTROLUMINESCENT LAYER, SAID OUTPUT VOLTAGES BEING FUNCTIONS OF SAID APPLIED INPUT VOLTAGE SIGNALS, A LIKE PLURALITY OF VOLTAGE COMPARATORS EACH HAVING FIRST AND SECOND INPUTS, SAID FIRST INPUTS BEING COUPLED TO SAID REFERENCE VOLTAGE MEANS, MEANS COUPLING EACH OF THE OUTPUT TERMINALS OF SAID COMPUTING MEANS TO THE SECOND INPUT OF A CORRESPONDING ONE OF SAID VOLTAGE COMPARATORS, EACH OF SAID VOLTAGE COMPARATORS PRODUCING AN OUTPUT VOLTAGE WHEN THE VOLTAGE APPLIED TO ITS FIRST INPUT BEARS A PREDETERMINED RATIO TO THE VOLTAGE APPLIED TO ITS SECOND INPUT, AND MEANS COUPLING THE OUTPUT OF EACH OF SAID VOLTAGE COMPARATORS TO A CORRESPONDING ONE OF SAID ELECTRODES. 